v3.8.0.1
Securities - Schedule of Securities in a Continuous Unrealized Loss Position Aggregated by Investment Category and Length of Time (Details) - USD ($)
$ in Thousands
Dec. 31, 2017
Dec. 31, 2016
Schedule Of Available For Sale Securities [Line Items]    
Less than 12 months, Fair Value $ 159,181 $ 464,524
Less than 12 months, Unrealized Loss (1,396) (9,784)
12 months or more, Fair Value 268,247  
12 months or more, Unrealized Loss (7,898)  
Total, Fair Value 427,428 464,524
Total, Unrealized Loss (9,294) (9,784)
U.S. Treasury Securities    
Schedule Of Available For Sale Securities [Line Items]    
Less than 12 months, Fair Value 197 297
Less than 12 months, Unrealized Loss (2) (3)
12 months or more, Fair Value 296  
12 months or more, Unrealized Loss (4)  
Total, Fair Value 493 297
Total, Unrealized Loss (6) (3)
Agency Mortgage-backed Securities    
Schedule Of Available For Sale Securities [Line Items]    
Less than 12 months, Fair Value 158,984 445,591
Less than 12 months, Unrealized Loss (1,394) (7,414)
12 months or more, Fair Value 259,213  
12 months or more, Unrealized Loss (6,005)  
Total, Fair Value 418,197 445,591
Total, Unrealized Loss (7,399) (7,414)
Beneficial interest - FHLMC securitization    
Schedule Of Available For Sale Securities [Line Items]    
Less than 12 months, Fair Value   18,636
Less than 12 months, Unrealized Loss   (2,367)
12 months or more, Fair Value 8,738  
12 months or more, Unrealized Loss (1,889)  
Total, Fair Value 8,738 18,636
Total, Unrealized Loss $ (1,889) $ (2,367)